A number of materials and methods have been developed for transferring substances from a gel or culture medium to an immobilizing membrane.
E. M. Southern (J. Molecular Biology, Vol. 98, p. 503, 1975) has disclosed a method for transferring nucleic acids from electrophoresis gels to an adsorptive medium. In the Southern method, the membrane is placed between the gel and a few layers of paper towels. As buffer solution is forced through the gel and membrane and into the paper towels by capillary action, the nucleic acid sample is driven into and deposited on the membrane. This is referred to as transfer by blotting.
Bittner et al. (Anal. Biochem., Vol. 102, p. 459, 1980) disclosed a similar method in which an electrical potential is used drive the nucleic acid sample into the membrane. This is referred to as electrophoresis transfer or electroblotting.
Adsorptive microporous membranes have also been used to transfer bacteria and viruses from growth media.
Several materials have been effectively used for use as transfer membranes, including nitrocellulose, nitrobenzyloxymethyl cellulose, aminobenzyloxymethyl cellulose, aminophenyl-thioether cellulose, diethylaminoethyl cellulose, and polyvinylidene fluoride. The cellulose-based materials are however brittle and frequently break up during the transfer process or the manipulations involved in subsequent analytical procedures.
U.S. Pat. No. 4,455,370 broadly discloses the use of microporous adsorptive nylon films as transfer films.
Methods for plasma-etching polyolefins in the presence of ammonia are, of course, known in the art.
U.S. Pat. No. 4,340,479 discloses a process for preparing skinless hydrophilic alcohol-insoluble polyamide membranes comprising preparing a solution of an alcohol-insoluble polyamide resin in a polyamide resin solvent, inducing nucleation of the solution by controlled addition of a nonsolvent for the polyamide resin to the polyamide resin solution to obtain a visible precipitate of polyamide resin particles, thereby forming a casting solution; spreading the casting solution on a substrate to form a film on the substrate, contacting and diluting the film of casting solution with a nonsolvent for the polyamide resin, thereby forming a membrane, washing the membrane to remove solvent, and drying the resulting membrane. The reference teaches that although the starting polymers are available in a wide variety of grades, which vary appreciably with respect to molecular weight and in other characteristics, the formation of a hydrophilic membrane appears to be a function not of these characteristics, but of the chemical composition of the polymer.
U.S. Pat. No. 3,876,738 discloses a process for the production of microporous films by casting or extruding a solution of a film-forming polymer in a solvent system into a quenching bath which is comprised of a nonsolvent system for the polymer. The polymers employed are preferably nylon polymers. There is no discussion of advantages which might accrue to the use of various molecular weight grades of nylon.